The present invention is a fibrous web product with a surface treatment containing bacterial cellulose and a method of surface treating such fibrous webs with bacterial cellulose. A particularly useful bacterial cellulose is one formed in aerated, agitated culture using a microorganism of the genus Acetobacter genetically selected for cellulose production under agitated conditions. Papers having the bacterial cellulose surface treatment have printing characteristics which approach or equal high quality coated offset papers.
It has been known for many years that cellulose can be synthesized by certain bacteria, particularly those of the genus Acetobacter. However, taxonomists have been unable to agree upon a consistent classification of the cellulose producing species of Acetobacter. For example, the cellulose producing microorganisms listed in the 15th Edition of the Catalog of the American Type Culture Collection under accession numbers 10245, 10821 and 23769 are classified both as Acetobacter aceti subsp. xylinum and as Acetobacter pasteurianus. For the purposes of the present invention any species or variety of bacterium within the genus Acetobacter that will produce cellulose under agitated conditions should be regarded as a suitable cellulose producer for the purposes of the present invention.
Acetobactor aceti subsp. xylinium is normally cultured under static conditions with the cellulose microfibrils being produced at the air medium interface. Most bacteria of this species are very poor cellulose producers when grown in agitated culture. One reason proposed for such poor production is that an agitated culture induces a tendency to mutation to noncellulose producing strains. In contrast, the Acetobacter strains according to the present invention are characterized by an ability to produce large amounts of cellulose in agitated culture without manifesting instability leading to loss of cellulose production in culture.
An earlier United States patent application, Ser. No. 788,915, filed Oct. 18, 1985 disclosed Acetobacter varieties which are vigorous cellulose producers under agitated culture conditions. The cellulose produced by the microorganisms and culture conditions disclosed in this application appears to be a unique type, physically quite different from the bacterial cellulose produced in static cultures. It has a highly branched, three dimensional, reticulated structure. A normal cellulose pellicle produced in static culture tends to have a lamellar structure with significantly less branching. The present invention involves the use of bacterial cellulose produced by such microorganisms under agitated conditions as a surface treatment for fibrous webs.
The need for static conditions for production of cellulose is disclosed in U.S. Pat. No. 4,588,400 (filed Dec. 16, 1982), which maintains the culturing material in a substantially motionless condition during cell growth and cellulose production. U.S. Pat. No. 4,588,400 describes formation of a bacterial pellicle, under static or motionless conditions, which is ultimately said to be usable as a wound dressing. Intermittent agitation produces fibrils of finite length which is determined by the linear extension rate of the fibril and the period between agitative shearing of the fibril from the surface of the microorganism. Nothing, however, is disclosed about the effects of continuous agitation on the cellulose product or about the production of a highly branched, three dimensional, reticulated fibrillar structure under either static or agitated conditions, nor about the use of bacterial cellulose as a surface treatment for fibrous webs.